The present invention relates to power control systems which comprise a prime mover and a generator driven by the prime mover. For instance, in a vehicle, an internal combustion engine provides mechanical power to propel the vehicle, and to drive engine accessories, such as generators, air conditioning units, compressors, cooling fans, and pumps, to name a few examples. In a generator set, an internal combustion engine drives a generator to convert the engine's mechanical power into electrical power. The present invention specifically focuses on a control device that controls the engine output power in order to enhance the performance of both the engine and generator. In particular, the control device is configured to ascertain a power level of the generator and to vary the output power of the engine so that the generator power level is maintained within a pre-determined range.
Electro-mechanical power conversion systems, such as those mentioned above, are normally comprised of an internal combustion engine and a generator. The engine supplies the generator with mechanical power where it is converted to electrical power. In a vehicle, for instance, the generator generates electrical power for the vehicle electrical system when the vehicle's engine is operating. In a generator set, the engine's mechanical power is converted to electrical power by the generator which is available via power output connectors. As electrical loads are added and removed from the generator, the engine experiences the corresponding variation in mechanical loads. In the case of the vehicle, during idle periods, such variations in mechanical loads on the engine cause the engine's rotational speed, commonly referred to as the RPM (revolution per minute) to vary accordingly. In the case of the generator set, similar changes in the RPM occur as electrical loads are connected and disconnected with the power output connectors.
Generator output power is typically a function of the generator shaft speed and it can be characterized by two distinct regions throughout the engine RPM range. In the first region, where the engine RPM ranges from 0 to approximately the idle RPM, the generator output power rate of change varies substantially with respect to the RPM. In the second region, where the engine RPM ranges from approximately the idle RPM to maximum RPM, the generator output power rate of change varies much less. Power conversion systems, such as those mentioned above, are devised taking these two regions into consideration. In the vehicle, the generator is selected based on the output power it can generate at idle RPM. In the generator set, the engine RPM is preset at a position where the engine produces its maximum output power and the generator is designed to produce its optimum power output at that RPM. As will be discussed below, such power conversion systems, without proper control of the engine in response to generator electrical output, may be detrimental to the system electrical components, are fuel inefficient, and may produce excessive noise.
A vehicle's engine RPM, at idle condition, varies as electrical loads are applied to and removed from the generator. The generator's output power is especially susceptible to such variations in the low RPM region. Even a small change in the engine RPM, for instance a 10% change, may produce a substantial variation in the generator output power, for instance a 30% change. Of particular concern is when the engine idle RPM is at a point where the generator can not produce enough power to meet the electrical demand.
When the electrical power demand surpasses the generator capacity at the operating RPM, the generator voltage decreases and supplemental energy is supplied by the vehicle battery to satisfy the electrical demand. This condition may be detrimental to the vehicle electrical system as the depleting battery energy causes a continuing decline in the system voltage.
In most applications, substantial electrical power demand on the vehicle electrical system occurs when the vehicle engine is at idle. As discussed above, increasing the electrical loads at engine idle RPM will cause the generator to reach a point where it can no longer sustain the system voltage even though the generator electrical output is below its rating. This is because the generator published rating applies to a much higher generator shaft speed. As this condition continues, the battery discharges and it will eventually reach a point of discharge detrimental to the battery life. Other electrical devices included in the vehicle electrical system may also malfunction when the system voltage falls below a certain threshold. For instance, most semiconductor-based electronic devices are designed to be deactivated when a low system voltage is detected.
In some other applications, a remote switch is provided to manually control the engine idle RPM. When the vehicle operator notices a drop in the system voltage, he may set a throttle cable or activate a switch which causes the engine RPM to increase in a discrete step. This in turn causes the generator RPM to increase, thus maintaining the system voltage. This higher RPM setting is commonly referred to as the high idle RPM. However, as the electrical loads are removed, the high idle RPM is no longer required to maintain the system voltage. Furthermore, the operator is typically not notified of this condition and the consequences are inefficient fuel consumption at high engine idle and low electrical load.
In a generator set, the power conversion system is designed such that the engine RPM is preset at a position that enables the generator to produce its maximum power. However, there are periods when the applied electrical loads do not require the engine to operate at this governed RPM. This condition gives rise to higher than needed fuel consumption. Furthermore, audible noise associated with the engine and/or the generator increase substantially with increasing RPM.
Although various systems have been proposed which touch upon some aspects of the above problems, they do not provide solutions to the existing limitations in power control systems. A common theme of these various systems is that the idle speed of an engine, driving an alternator, is manipulated in response to variations of battery voltage, system electrical loads and mechanical loads on the engine by the generator.
For example, the Fenley patent, U.S. Pat. No. 5,570,001, discloses an apparatus that includes an engine driving an alternator where the engine speed is automatically controlled by manipulating the throttle according to the charging current of the alternator. The apparatus is further capable of unloading the alternator from the engine when excessive electrical loads are engaged, in order to prevent the engine from stalling. However, this apparatus does not recognize an idle condition of the engine and therefore it cannot be used in a motor vehicle that is propelled via a transmission. Furthermore, the throttle control of this apparatus is based on charging current of the alternator while the present invention controls the throttle according to a power level of the alternator which includes voltage, current, and duty cycle.
In DeBiasi et al., U.S. Pat. No. 5,481,176, the disclosure describes a charging system including an engine driving an alternator and a voltage regulator, where the voltage regulator voltage set-point is modified by an engine controller device according to (1) near-wide-open-throttle, (2) application of vehicle brakes, and (3) increased torque of the alternator, or any combination thereof. When condition (3) is met, the engine controller manipulates the engine idle speed to keep it relatively constant as the applied electrical loads cause the alternator's torque on the engine to increase. However, this charging system reduces the voltage regulator voltage set-point when electrical loads are applied, causing the system voltage to go down and subsequently ramps up the voltage set-point to its initial setting while adjusting the throttle, so that the idle speed remains relatively unaffected by increased electrical loads. The present invention manipulates the throttle to maintain both the idle speed and system voltage constant in light of increased or decreased electrical loads.
Center et al., U.S. Pat. No. 5,402,007, discloses an apparatus including an engine driving an alternator, where the system voltage set-point is determined during off-idle operation (“off-idle voltage”) and compared with a voltage measured during idle operation (“idle voltage”). The throttle is then manipulated such that the measured voltage is equal to the system voltage set-point. However, this apparatus requires the system voltage set-point to be determined separately while the present invention is pre-programmed with the system voltage set-point. Furthermore, the throttle is manipulated based on the difference between the off-idle voltage and idle voltage, while the present invention controls the throttle based on the alternator power level which includes voltage, current, and duty cycle.
Power conversion systems, such as those incorporated in a vehicle or a generator set, utilize a prime mover and a generator. An important aspect of the control of such power conversion systems is monitoring the output power of the prime mover and the power level of the generator. Only then can proper operation of the electrical and/or mechanical components, efficient fuel consumption, and audible noise reduction be assured. Considering these issues, a control device is needed to monitor the engine and the generator, and to vary the engine output power based on the power level of the generator.